A data storage device, such as solid state drive (SSD), secure digital (SD) memory card or portable flash memory, is mainly constituted of a control unit and a data storage medium. The data storage medium is constituted of a plurality of data columns for storing data.
Inevitably, secondary products may be produced in the manufacturing process of data storage devices. Therefore, it is necessary to screen out all bad data columns in the data storage medium and label or record (by using software, for example) the bad data columns in a bad data column table before releasing the secondary products to the market. According to the bad data column table, the control unit is prevented from accessing the labeled bad data columns so as to avoid data access error during operation.
Conventionally, bad data columns are labeled or recorded one by one. However, the number of available labels or records for bad data columns is limited (for example, 254 labels at most). Therefore, if the data storage medium is largely defective, the available labels for bad data columns may be used up and the resulting unlabeled or unrecorded bad data columns may reduce the correcting capability (e.g., 44-bit correction) of the ECC (Error Correcting Code), thus leading to improper corrections of data that could have been properly corrected.